In resistive ribbon thermal dye transfer, a ribbon made from a resistive support, a conducive layer, and a dye-containing layer is placed face-to-face with a dye-receiving element. Current is supplied to the resistive support by an electrode or array of electrodes and returns to ground via the conductive layer. The electric current is converted to heat through the resistive heating of the ribbon, and the hat causes dye in the dye-containing layer to be transferred to the dye-receiving element through the processes of dye diffusion, dye sublimation, or melting of the dye-containing layer. By imagewise controlling the current supplied, a desired dye image can be transferred.
Dye transfer may be performed as an essentially binary process, wherein the effect of the applied current is to transfer either all or none of the dye in the dye layer at the point where the current is supplied. Wax transfer is an example of such a binary process. Alternatively, the current applied to the electrodes may be varied in order to control the heat levels applied to the transferable dye and thereby control the amount of dye transferred in order to form continuous tone images of variable dye density. U.S. Pat. No. 4,800,399 discloses such a continuous tone resistive ribbon printing system, the disclosure of which is hereby expressly incorporated by reference.
During the resistive ribbon thermal dye transfer process, the resistive support comes in contact with the printing electrode(s) which supply the current. In order to reduce ribbon and printing electrode damage, reduce friction, and loosen material which builds up at the printing electrodes, it is known to use graphite as a coating on the resistive ribbon in a binary process as disclosed in U.S. Pat. No. 4,477,198 (Bowlds et al.). While graphite is a well-known solid lubricant, its use as a coating or "slipping " layer does not give a satisfactory image quality in application to continuous one resistive ribbon color printing.
Liquid lubricants have been suggested for use in slipping layers for thermal dye transfer using thermal heads, e.g. Japanese Kokais No. 59-196291 (Matsushita Electric Ind.) and No. 690-2297595 (Matsushita Electric Ind.; Mitsubishi Chem. Ind.), but the prior art does not suggest their use in resistive ribbon technology nor the superior results obtained in resistive ribbon technology as compared to use of solid lubricants.